For many years this was enough to make the company's stock price rise, as companies were often valued largely on their return on investment. The aggressive nature of the conglomerators themselves was enough to make many investors, who saw a "powerful" and seemingly unstoppable force in business, buy their stock. High stock prices allowed them to raise more loans, based on the value of their stock, and thereby buy even more companies. This led to a chain reaction, which allowed them to grow very rapidly.

However all of this growth was somewhat illusory and when interest rates rose to offset inflation, conglomerate profits fell. Investors noticed that the companies inside the conglomerate were growing no faster than before they were purchased, whereas the rationale for buying a company was that "synergies" would provide efficiency. By the late 1960s they were shunned by the market, and a major sell-off of their shares ensued. To keep the companies going, many conglomerates were forced to shed the industries they had recently purchased, and by the mid-1970s most had been reduced to shells.[2] The conglomerate fad was subsequently replaced by newer ideas like focusing on a company's core competency.

In other cases, conglomerates are formed for genuine interests of diversification rather than manipulation of paper return on investment. Companies with this orientation would only make acquisitions or start new branches in other sectors when they believed this would increase profitability or stability by sharing risks. Flush with cash during the 1980s, General Electric also moved into financing and financial services, which in 2005 accounted for about 45% of the company's net earnings. GE formerly owned a minority interest in NBCUniversal, which owns the NBCtelevision network and several other cable networks. In some ways GE is the opposite of the "typical" 1960s conglomerate in that the company was not highly leveraged, and when interest rates went up they were able to turn this to their advantage. It was often less expensive to lease from GE than buy new equipment using loans. United Technologies has also proven to be a successful conglomerate.

With the spread of mutual funds (especially index funds since 1976), investors could more easily obtain diversification by owning a small slice of many companies in a fund rather than owning shares in a conglomerate. Another example of a successful conglomerate is Warren Buffett's Berkshire Hathaway, a holding company which used surplus capital from its insurance subsidiaries to invest in a variety of manufacturing and service businesses.

The end of the First World War caused a brief economic crisis in Weimar Germany, permitting entrepreneurs to buy businesses at rock-bottom prices. The most successful, Hugo Stinnes, established the most powerful private economic conglomerate in 1920s Europe – Stinnes Enterprises – which embraced sectors as diverse as manufacturing, mining, shipbuilding, hotels, newspapers, and other enterprises.

The best known British conglomerate was Hanson plc. It followed a rather different timescale than the US examples mentioned above, as it was founded in 1964 and ceased to be a conglomerate when it split itself into four separate listed companies between 1995 and 1997.

In Japan, a different model of conglomerate, the keiretsu, evolved. Whereas the Western model of conglomerate consists of a single corporation with multiple subsidiaries controlled by that corporation, the companies in a keiretsu are linked by interlocking shareholdings and a central role of a bank. Mitsubishi is one of Japan's best known keiretsu, reaching from automobile manufacturing to the production of electronics such as televisions.

In South Korea, the chaebol are a type of conglomerate owned and operated by a family. A chaebol is also inheritable, as most of current presidents of chaebols succeeded their fathers or grandfathers. Some of the largest and most well-known Korean chaebols are Samsung, LG, Hyundai Kia and SK.

In New Zealand, Fletcher Challenge was formed in 1981 from the merger of Fletcher Holdings, Challenge Corporation, and Tasman Pulp & Paper, in an attempt to create a New Zealand-based multi-national company. At the time, the newly merged company dealt in construction, building supplies, pulp and paper mills, forestry, and oil & gas. Following a series of bungled investments, the company demerged in the early 2000s to concentrate on building and construction.

Diversification results in a reduction of investment risk. A downturn suffered by one subsidiary, for instance, can be counterbalanced by stability, or even expansion, in another division. For example, if Berkshire Hathaway's construction materials business has a good year, the profit might be offset by a bad year in its insurance business. This advantage is enhanced by the fact that the business cycle affects industries in different ways. Financial Conglomerates have very different compliance requirements from insurance or reinsurance solo entities or groups. There are very important opportunities that can be exploited, to increase shareholder value.

A conglomerate creates an internal capital market if the external one is not developed enough. Through the internal market, different parts of conglomerate allocate capital more effectively.

A conglomerate can show earnings growth, by acquiring companies whose shares are more discounted than its own. In fact, Teledyne, GE, and Berkshire Hathaway have delivered high earnings growth for a time.[4]

Accounting disclosure is less useful information, many numbers are disclosed grouped, rather than separately for each business. The complexity of a conglomerate's accounts make them harder for managers, investors and regulators to analyze, and makes it easier for management to hide things.

Conglomerates can trade at a discount to the overall individual value of their businesses because investors can achieve diversification on their own simply by purchasing multiple stocks. The whole is often worth less than the sum of its parts.

Brand dilution where the brand loses its brand associations with a market segment, product area, or quality, price or cachet.

Some cite the decreased cost of conglomerate stock (a phenomenon known as conglomerate discount) as evidential of these disadvantages, while other traders believe this tendency to be a market inefficiency, which undervalues the true strength of these stocks.[10]

Time Warner included several tenuously linked businesses during the 1990s and 2000s, including Internet access, content, film, cable systems and television. Their diverse portfolio of assets allowed for cross-promotion and economies of scale. However, the company has sold or spun off many of these businesses – including Warner Music Group, Warner Books, AOL, Time Warner Cable, and Time Inc. – since 2004.

Clear Channel Communications, a public company, at one point owned a variety of TV and radio stations and billboard operations, together with a large number of concert venues across the U.S. and a diverse portfolio of assets in the UK and other countries around the world. The concentration of bargaining power in this one entity allowed it to gain better deals for all of its business units. For example, the promise of playlisting (allegedly, sometimes, coupled with the threat of blacklisting) on its radio stations was used to secure better deals from artists performing in events organized by the entertainment division. These policies have been attacked as unfair and even monopolistic, but are a clear advantage of the conglomerate strategy. On December 21, 2005, Clear Channel completed the divestiture of Live Nation, and in 2007 the company divested their television stations to other firms, some which Clear Channel holds a small interest in. Live Nation owns the events and concert venues previously owned by Clear Channel Communications.

Quebecor Media, a Canadian company controlling a subset of TV and radio stations, print magazines and newspaper, software company and a 4-play telecom company

Impact of Conglomerates on the Media: The six major media conglomerates in the United States are The Walt Disney Company, General Electric, News Corporation, Viacom, Time Warner and CBS. The Walt Disney Company is linked with ABC Television group, creating the largest media corporation, with revenue equal roughly thirty six billion dollars. Since Walt Disney owns ABC, it directly controls what shows and news is shown. General Electric owns NBC, and does not allow any negative reporting against General Electric on air. Viacom’s chief executive, Sumner Redstone, considers himself a “liberal democrat” and most of the programs shown have a primarily liberal perspective.[11]

Media Conglomerate Impact on Journalism: It leads to opinionated journalism versus traditional journalism. Opinionated journalism is is a journalist adding his or her ideologies on a matter on top of reporting it to the public. The coverage that conglomerates have of issues, especially political, is not necessarily objective, and fails to report both sides of an issue, if not taking a neutral stance.[12] This is known as media bias. Media bias is ”the intentional or unintentional slanting of news reporting toward one side due political views or cultural beliefs of journalists, producers or owners of a media outlet.[11]”

Although a relatively new development, Internet conglomerates, such as Alphabet, Google's parent company[13] belong to the modern media conglomerate group and play a major role within various industries, such as brand management. In most cases Internet conglomerates consist of corporations who own several medium-sized online or hybrid online-offline projects. In many cases, newly joined corporations get higher returns on investment, access to business contacts, and better rates on loans from various banks.[citation needed]